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Show 1906.] OF MONKEYS IN THE MENAGERIE. 559 Needless to add, this is hardly the classification to be expected on a priori grounds from the usually accepted views of the affinities of the species concerned. It seems to me to be probable that the swelling will be found to be characteristic of all the species of Mangabeys and Baboons ; but in the case of the Macaques no generalisations can be drawn until further observations have been made. In 1904 I recollect seeing in the Berlin Gardens a female Macaque of a species whose name I have now forgotton, with the swelling like that of M. nemestrinus. Thus at least two species of this genus fall under section a of the above-given table. On the other hand, it is by no means certain that all the forms related to rhesus and fusccitus can be ranged with these species under section a . For example, P. L. Sclater (P.Z.S. 1864, p. 710) says that a female of the Formosan Macaque (M. cyclopis) upon reaching maturity " acquired a most extraordinary development of the parts surrounding the organs of generation." The figure that accompanies this description, however, shows a long lobate swelling extending on each side down the back of the thigh and along the proximal third of the tail-a development quite unlike anything known to me in other species. It is significant, too, that Sclater speaks of this swelling as if it were permanent and not periodic. If permanent the development must probably be of a different kind from that now under discussion. If periodic and connected with menstruation it must indicate an important physiological difference between M. cyclopis and M. rhesus, two species structurally somewhat nearly related. The swelling may be nothing but a useless correlative or accompaniment of the physiological processes incidental to menstruation. But, in my opinion, the development of a highly vascular, sensitive, and thin-skinned outgrowth of this nature-an obvious inconvenience to the monkey, since it involves special precautions to prevent injury, impairs activity, and is liable to laceration when quarrels arise-probably, rather than otherwise, carries with it some compensating advantage to the species. What may this be ? Possibly the following considerations may throw some light on the subject. The similarity in form and colour between male and female Monkeys leaves no clue to the sex of a particular individual when seen at a distance. The males, moreover, are not apprised by the sense of smell of the condition of the females when " on heat as are the males or Carnivora Ungulata, Kodentia, and of other orders of Mammals. Hence it may be that the function of the swelling in question is to serve as a source of information to the males on the two points mentioned above. I think it may be claimed that such information is of use for the maintenance of the species. But whethei the usefulness in these particulars of the swelling be or be not the factor that has guided its evolution, it is difficult to see how such a coloured excrescence can fail to convey the said information in the case of animals so intelligent and keen-sighted as Monkeys. For as is fully attested by flowers like scarlet geraniums and by P hoc. Z ool. S oc.- 1906, No. XXXVIIJ. 38 |